A community’s interactions include competition, predation herbivory, symbiosis and disease.
What is a community? Give three types of symbiosis here.
The purpose of this study material is to give you an insight into and knowledge of the way in which an ecosystem works. A community’s interactions include competition, predation, hebivory, symbiosis and disease.
Learning outcome 6:
Discuss/explain the biodiversity and complexity of crea- tion and methods for sustaining them.
You will know that you have achieved this learning outcome if you are able to: explain the difference between a community and a population
list four possible specific interactions and explain how the relationships affect the population densities of the two species
explain how interspecific competition may affect community structure
describe the competitive exclusion principle and explain how competitive exclusion may affect community structure
define an ecological niche and restate the competitive exclusion principle using the niche concept
define and compare predation, herbivory and parasitism
relate some specific predatory adaptations to the properties of the prey
describe the defence mechanisms that have evolved in plants to reduce predation by herbivores
describe how predators use mimicry to obtain prey
B
a
si
c B
iolo
g
y
Ba
sic
B
io
log
y
B
a
si
c B
iolo
g
y
distinguish among endoparasites, ectoparasites and pathogens distinguish among parasitism, mutualism and commensalism distinguish between a food chain and a food web
describe the factors that transform food chains into food webs
TEXTBOOK READING:
Study the section that discusses the way a community’s interactions in- clude competition, predation, herbivory, symbiosis and disease, in Reece et al (2011) pages 1240–1246, under the following headings:
¡ Competition: Interspecific competition occurs when species compete for a particular resource that is in short supply. The competitive exclusion principle: One species uses resources more efficiently and thus reproduces more rapidly than the other, which can lead to the elimination of the second species.
Ecological niche: The sum total of a species’ use of the biotic and abiotic resources in its environment is called the species’ ecological niche.
Resource partitioning: When competition between two species having identical niches does not lead to local extinction of either species, it is generally because one species niche becomes modified.
Character displacement. What are allopatric and sympatric populations? Figure 53.4 explains character displacement using an example.
¡ Predation: What is a predator? You should be able to discuss predator adaptation, plant defences against herbivores, animal defences against predators and parasites and pathogens.
¡ Herbivory: The interaction during which a herbivore eats a plant. Can plants avoid being eaten?
¡ Parasitism: Symbiotic interaction in which the parasite derives nourishment from a host, which is harmed in the process. What is an endoparasite and an ectoparasite? ¡ Disease: Pathogens or disease-causing agents, mostly microscopic and usually lethal ¡ Mutualism: You should be able to define mutualism and give an example.
BL G 15 01/ 1
STUDY UNIT 14.2
Diversity and trophic structure characterise biological communities. Learning outcome 6.
Discuss/explain the biodiversity and complexity of crea- tion and the methods for sustaining them.
You will know that you have achieved this learning outcome if you are able to: explain what species diversity is
describe the trophic structure of a community explain what dominant and keystone species are
explain the difference between a bottom-up and a top-down model
TEXTBOOK READING:
Study the section on the diversity and trophic structure that characterise biological communities in Reece et al (2011), pages 1246 –1252 under the following headings:
¡ Species diversity: This is the variety of different organisms that make up a commu- nity. It has two components – species richness and relative abundance (see fig 54.10). ¡ Diversity and community stability: Ecologists examine the potential benefits of
diversity, including the increased productivity and stability of biological communities. Figure 54.12 shows the site of long-term experiments on manipulating plant diversity. ¡ Trophic structure: The structure and dynamics of a community that depend largely
on the feeding relationship between organisms.
Food webs: Figures 54.14 and 54.15 give examples of food webs.
Limits on food chain lengths: Each food chain within a food web is usually only a few links long. Read through the rest of this paragraph for background knowledge.
¡ Species with a large impact
Dominant species are those species in a community that are the most abundant or that collectively have the highest biomass. Do you know what invasive species are?
Keystone species are not necessarily abundant in a community, but exert strong control on community structure (see figs 54.17 and 54.18).
Ecosystem engineers (foundation species) are species that exert their influence not through their trophic interactions but by causing physical changes in the environment that affect the structure of the community.
Bottom-up and top-down controls: You should be able to explain briefly the difference between a bottom-up and a top-down model.
STUDY ACTIVITY 14.2
Complete concept check 54.2, numbers 1 and 2, on page 1252 of the textbook.
FEEDBACK
For suggested answers see Appendix A at the back of the textbook.
STUDY UNIT 14.3
Disturbance and influences species diversity and composition Learning outcome 6:
Discuss/explain the biodiversity and complexity of crea- tion and the methods for sustaining them.
You will know that you have achieved this learning outcome if you are able to: explain what species diversity is
describe how disturbances affect community structure and composition. Illustrate this point with several well-studied examples.
give examples of humans as widespread agents of disturbance describe and distinguish between primary and secondary succession
TEXTBOOK READING:
Study the section on disturbance and the influences on species diversity and composition, in Reece et al (2011), pages 1253–1256, under the fol- lowing headings:
¡ What is a disturbance? What is a disturbance? Give an example of a disturbance in your own environment? Read through the rest of the paragraph for background knowledge.
BL G 15 01/ 1
STUDY UNIT 14.5
Community ecology is useful for understanding pathogen life cycles and con- trolling human disease.
Read this section for background knowledge. INDIVIDUAL EXERCISE
Complete the Test your understanding quiz on page 1263 of the textbook (Campbell 2011), numbers 11 and 12.
FEEDBACK
Answers to the self-quiz questions are provided in Appendix A at the back of the textbook. REFLECT ON YOUR LEARNING
¡ Check the answers and mark your own attempts. ¡ Make sure that you have mastered the outcomes. ¡ Work through the Chapter review on p 1262. EVALUATION QUESTIONS
The evaluation questions will help you to determine whether you have mastered all the outcomes. You should submit some of the questions for evaluation. Please refer to Tutorial Letter 101 for the details of Assignment 02.
14.1 Give an example of a community from your own environment. (2) 14.2 Explain the difference between a community and a population. (2) 14.3 List four possible specific interactions and explain how each of the relation-
ships affect the population densities of the species. (8) 14.4 Give an example of interspecific competition in your own environment and
explain how it may affect community structure. (3) 14.5 Describe the competitive exclusion principle and explain how competitive
exclusion may affect community structure. (4) 14.6 Define an ecological niche. (2) 14.7 Explain how resource partitioning can affect species diversity. (2) 14.8 Define predation, herbivory and parasitism. (3) 14.9 Name three defence mechanisms that have evolved in plants to reduce
predation by herbivores. (2)
14.10 Give an example of how predators use mimicry to obtain prey. (1) 14.11 Distinguish among endoparasites, ectoparasites and pathogens. (3) 14.12 Distinguish among parasitism, mutualism, and commensalism. (3) 14.13 Distinguish between a food chain and a food web. (2)
14.14 Give an example of how disturbances affect community structure and
composition in your own environment. (3) 14.15 Give an example of where humans have acted as agents of disturbance
in your own community. (1)
14.16 Describe and distinguish between primary and secondary succession. (3) 14.17 Distinguish between species richness and relative abundance. (2)
BL G 15 01/ 1